Some data processing systems that receive stored or transmitted electronic data use sampling circuits to generate a digital representation of the electronic data. To assist the data processing system to sample the electronic data at the correct frequency and phase. A timing error detector determines when the sampling is performed at an incorrect frequency or phase. In some instances, a preamble pattern is inserted into the electronic data, enabling the timing error detection. However, after the preamble pattern has ended, timing errors can reoccur due to intrinsic timing drift in the system, characteristics of the storage or transmission medium, and the environment of the data processing system.